1. Field of the Invention
The present invention relates to a mobile body communication device for performing communication between a plurality of mobile bodies such as construction machines and a terminal device.
2. Description of the Related Art
Data such as a service meter indicating the state of operations (state of halted operations) in a mobile body, particularly a construction machine, are necessary information for managing a vehicle or for labor management of workers.
As conventional methods of obtaining information relating to a construction machine, a maintenance engineer travels to the site of the construction machine and performs a visual check, or a personal computer is connected to the construction machine such that history data written into memory in the interior of the construction machine are downloaded. A plurality of construction machines are managed by storing data accumulated from the plurality of construction machines in the memory of a computer in an administrative bureau.
Since information gathering is performed by human labor, however, this information gathering becomes more complicated as the number of construction machines increases and the locations thereof become more remote, and thus the working efficiency of information gathering is greatly diminished.
Hence, as is described in Japanese Patent Application Laid-Open No. 6-330539 and so on, endeavors have been made to perform construction machine information gathering automatically using communication means, without relying upon human labor.
In the invention described in the aforementioned patent application, an management unit and a construction machine are connected by communication means so as to be capable of bidirectional communication, whereby a data request is transmitted from the management unit and data are extracted from the construction machine and returned to the management unit. In this manner, information on the construction machine side is accumulated in a requesting management unit. As a result, construction machine information can be obtained by a terminal on the management unit side only when a request is placed by the management unit side.
It is therefore desirable for data indicating the state of operations (state of halted operations) in a construction machine to be accumulated, and for these accumulated data to be periodically (for example once a day) inspected on the side of an administrator.
According to the invention described in the aforementioned patent application, however, construction machine data are only obtained on the administrator side when a request is placed from the management unit to the construction machine, and therefore the desire noted above to enable operational state data accumulated in the construction machine to be periodically inspected on the administrator side cannot be fulfilled.
Furthermore, no particular problem arises when operational state data are transmitted periodically (for example once a day) from one construction machine to the administrator side, but when data from a plurality of construction machines are transmitted all at once at a specific time, communication lines become congested, leading to possible impediments such as communication delays.
It is therefore possible to set different transmission time data in each of the plurality of construction machines. In so doing, however, software containing different transmission time data must be individually installed in each construction machine. As a result, parts cannot be standardized among the plurality of construction machines and overall system costs rise.
It is therefore an object of the present invention to avoid communication congestion by varying transmission times among a plurality of mobile bodies while maintaining standardization of the software to be installed in the plurality of mobile bodies.